鑽石舞台

When we park in a big parking lot, how do we remember where we parked our car? Here's the problem facing Homer. And we're going to try to understand what's happening in his brain. So we'll start with the hippocampus, shown in yellow, which is the organ of memory. If you have damage there, like in Alzheimer's, you can't remember things including where you parked your car. It's named after Latin for "seahorse," which it resembles.

當我們在大型停車場停車後，如何回憶起將車停在了哪個車位呢？這就是現在困擾荷馬的問題。接下來我們將嘗試了解此時他腦中正開展何種「運動」。我們先着眼於大腦海馬區，即黃色的區域，這是我們的記憶器官。如果海馬區出現損傷,像老年痴呆症患者一樣，你將喪失記憶力，乃至記不起將車停在了何處。這個詞源自拉丁語，有「海馬」之意因為腦中海馬區的形狀看上去有點像「海馬」。

And like the rest of the brain, it's made of neurons.So the human brain has about a hundred billion neurons in it. And the neurons communicate with each other by sending little pulses or spikes of electricity via connections to each other. The hippocampus is formed of two sheets of cells, which are very densely interconnected. And scientists have begun to understand how spatial memory works by recording from individual neurons in rats or mice while they forage or explore an environment looking for food.

海馬區和大腦其它區域的組成相似，都由神經元構成。人的大腦由大約一千億個神經元細胞組成。每個神經元細胞之間通過一些連接中介互相發送小的電脈衝或者尖峰電壓來進行「交流」。海馬區由兩層片狀的細胞群構成，這兩層細胞群緊密相連。科學家們通過記錄老鼠在某環境中搜羅食物時其腦中單個神經元細胞的反應來了解「空間記憶」的工作原理與工作機制。

So we're going to imagine we're recording from a single neuron in the hippocampus of this rat here. And when it fires a little spike of electricity, there's going to be a red dot and a click. So what we see is that this neuron knows whenever the rat has gone into one particular place in its environment. And it signals to the rest of the brain by sending a little electrical spike. So we could show the firing rate of that neuron as a function of the animal's location. And if we record from lots of different neurons,we'll see that different neurons fire when the animal goes in different parts of its environment, like in this square box shown here.

現在想象一下，我們正在為這隻老鼠的海馬區中的一個神經元細胞「錄像」。每當這個細胞發出小型尖峰電壓，隨後會出現一個紅點以及咔噠的一聲。我們可以看出每當老鼠進入環境中某一特定位置，這個神經元細胞便會有反應。然後這個細胞再通過小型尖峰電壓將以上信息傳遞給大腦的其它區域。這麼一來，我們可以憑藉這個細胞發送信號的頻率推知老鼠經過的相應位置。倘若我們記錄的是很多不同的神經元細胞，就會發現當老鼠處於不同的位置上時，不同的神經元細胞會產生各自的電信號，正如我們在這些方形中看到的那樣。

So together they form a map for the rest of the brain, telling the brain continually, "Where am I now within my environment?" Place cells are also being recorded in humans. So epilepsy patients sometimes need the electrical activity in their brain monitoring. And some of these patients played a video game where they drive around a small town. And place cells in their hippocampi would fire, become active, start sending electrical impulses whenever they drove through a particular location in that town. So how does a place cell know where the rat or person is within its environment?

這些信號為大腦中的其它區域勾勒出一張地圖，持續地向大腦指示出，「我現在位於環境中的哪個具體點上？」我們也記錄人腦中的「定位神經元細胞」。癲癇病患者有時需要監測他們的腦電活動情況。一些患者玩一種電子遊戲，遊戲中他們在一個小鎮上自由開車。然後當他們驅車駛過鎮上的某一處時，他們大腦海馬區中的「定位神經元細胞」便會被激活，發出信號。那麼這「定位細胞」是怎麼知道老鼠或人處於某個位置的呢？

Well these two cells here show us that the boundaries of the environment are particularly important. So the one on the top likes to fire sort of midway between the walls of the box that their rat's in. And when you expand the box, the firing location expands. The one below likes to fire whenever there's a wall close by to the south.And if you put another wall inside the box, then the cell fires in both place wherever there's a wall to the south as the animal explores around in its box. So this predicts that sensing the distances and directions of boundaries around you -- extended buildings and so on -- is particularly important for the hippocampus.

這裡有兩個神經元細胞，它們告訴我們，在定位時環境的邊界是至關重要的。上面的這個細胞傾向於在老鼠向盒子中部走去時產生信號。因此當你將盒子擴大，相應的信號活躍區也隨之擴大。下面的這個喜歡在老鼠緊鄰南面屏障時作出反應。因此當你在盒中放入另一屏障時，不論老鼠在盒中何處，只要它的南面有屏障，該細胞中的相應位置便會同時產生信號。這表明了解到達邊界——比如周邊的建築物等需要的距離和方向對於海馬區的「工作」而言至關重要。

And indeed, on the inputs to the hippocampus, cells are found which project into the hippocampus, which do respond exactly to detecting boundaries or edges at particular distances and directions from the rat or mouse as it's exploring around. So the cell on the left, you can see, it fires whenever the animal gets near to a wall or a boundary to the east, whether it's the edge or the wall of a square box or the circular wall of the circular box or even the drop at the edge of a table, which the animals are running around.

而且確實，在老鼠搜羅環境時，我們在海馬區的輸入信號中，檢測到能對距環境邊界的特定距離與方向作出精確感應的神經元細胞。這裡左邊的細胞，你可以看出，當老鼠向東靠近邊界或屏障時，該細胞都會作出反應，不論這邊界是一個方盒的邊還是一個圓柱盒的邊，甚至是老鼠繞着轉的桌布的垂簾。

And the cell on the right there fires whenever there's a boundary to the south, whether it's the drop at the edge of the table or a wall or even the gap between two tables that are pulled apart. So that's one way in which we think place cells determine where the animal is as it's exploring around. We can also test where we think objects are, like this goal flag, in simple environments -- or indeed, where your car would be. So we can have people explore an environment and see the location they have to remember.

而右面的細胞則是在老鼠南面出現邊界時響應，不論這邊界是桌布的垂簾還是一堵牆甚至是兩個被隔開的桌子之間的間隙。以上是我們所推測的一種「定位細胞」給動物定位的方式。我們也可檢測，人類在簡單環境中，是怎樣給——諸如這面旗這樣的物體定位的或者乾脆——把這物體想成你的車。我們先讓人們熟悉一下環境，同時記下物體所在的位置。

And then, if we put them back in the environment,generally they're quite good at putting a marker down where they thought that flag or their car was. But on some trials, we could change the shape and size of the environment like we did with the place cell. In that case, we can see how where they think the flag had been changes as a function of how you change the shape and size of the environment. And what you see, for example, if the flag was where that cross was in a small square environment, and then if you ask people where it was, but you've made the environment bigger, where they think the flag had been stretches out in exactly the same way that the place cell firing stretched out.

接着，再讓他們回到那個環境，通常他們都能根據記憶準確無誤地標出物體所在的位置。但在一些試驗中，我們會改變環境的形狀和尺度，正如我們在「定位細胞」實驗中所做的那樣。如此，我們可以通過研究實驗者改變環境的形狀和尺度，來了解旗幟發生了怎樣的位移。比如現在你所看到的，假設這面旗幟在如圖中小四方形內的「×」的位置，然後接着你問人們小旗在哪，但實際上你已經將總環境的尺度擴大了，結果他們所認為的旗所在的位置也相應地向外擴張，而這擴張的模式和「定位細胞」的一模一樣。

It's as if you remember where the flag was by storing the pattern of firing across all of your place cells at that location, and then you can get back to that location by moving around so that you best match the current pattern of firing of your place cells with that stored pattern. That guides you back to the location that you want to remember. But we also know where we are through movement. So if we take some outbound path -- perhaps we park and we wander off -- we know because our own movements, which we can integrate over this path roughly what the heading direction is to go back.

這就好像你是通過存儲被某一特定位置所激發的「定位細胞」產生的信號模式來記憶小旗的位置的，接着當你回到那個地點的時候，通過四處打量，便可以將你當前腦中「定位細胞」的信號模式與之前的模式進行匹配。這個過程便可讓你回到「老地方」。我們也能通過位移來給自己定位。因此當我們外出時——或許是我們停車後下來隨便走走——我們可以給自己定位，因為我們可以粗略地將自己的運動路線與大體的返回方向進行整合。

And place cells also get this kind of path integration input from a kind of cell called a grid cell. Now grid cells are found, again, on the inputs to the hippocampus, and they're a bit like place cells. But now as the rat explores around, each individual cell fires in a whole array of different locations which are laid out across the environment in an amazingly regular triangular grid. And if you record from several grid cells -- shown here in different colors -- each one has a grid-like firing pattern across the environment, and each cell's grid-like firing pattern is shifted slightly relative to the other cells.

「定位細胞」也能從一種叫做「網狀細胞」的細胞那兒獲得此類線路整合的信息。目前在向海馬區的信號輸入中又發現了「網狀細胞」，它們與「定位細胞」有點類似。隨着老鼠的「四處探索」，每一個神經元細胞被大量各種位置所激發的信號組合在一起，貫穿整個環境構成一個令人驚嘆的規整的三角網格。倘若你對一系列「網狀細胞」進行記錄——這裡以不同的顏色區分——每一個細胞發出的信號都能形成網狀，遍及整個環境，而且每一個細胞的網狀信號集的位置都與其他細胞有一定偏差。

So the red one fires on this grid and the green one on this one and the blue on on this one. So together, it's as if the rat can put a virtual grid of firing locations across its environment --a bit like the latitude and longitude lines that you'd find on a map, but using triangles. And as it moves around, the electrical activity can pass from one of these cells to the next cell to keep track of where it is, so that it can use its own movements to know where it is in its environment. Do people have grid cells?

因此紅色標註的細胞信號集合在這個網格上，綠色的是這個，而藍色的是這個。因此綜合來看，這就好像老鼠可以在它所到達的環境中建立一個虛擬的位置信號網——這就有點像你在地圖上所看到的經線和緯線，只不過要將線替換成「三角形」。當老鼠移動的時候，這些電信號能通過這些細胞傳遞給下一個神經元細胞從而為老鼠定位，這樣老鼠就能在運動時知道自己身在何處。那麼人類是否有「網狀細胞」呢？

Well because all of the grid-like firing patterns have the same axes of symmetry, the same orientations of grid, shown in orange here, it means that the net activity of all of the grid cells in a particular part of the brain should change according to whether we're running along these six directions or running along one of the six directions in between. So we can put people in an MRI scanner and have them do a little video game like the one I showed you and look for this signal. And indeed, you do see it in the human entorhinal cortex, which is the same part of the brain that you see grid cells in rats. So back to Homer.

因為所有的網狀信號集合體都有相同的對稱軸，以及相同的網格朝向，這裡以橘紅色標識，這就意味着大腦中特定部位的所有網狀細胞的聯網行為的變化應該取決於我們是在向着這六個方向運動還是沿着六個方向之間所夾的某一個方向運動。我們可以為人們做核磁共振掃描，與此同時讓他們玩一個小型電子遊戲，還是之前所說的那個遊戲，然後來看看當時的信號。沒錯，你在人腦中的內嗅皮層上看到了網狀細胞，而它們出現的位置和老鼠的網狀細胞在大腦中所出現的位置一樣。現在我們回頭看看荷馬。

He's probably remembering where his car was in terms of the distances and directions to extended buildings and boundaries around the location where he parked.And that would be represented by the firing of boundary-detecting cells. He's also remembering the path he took out of the car park, which would be represented in the firing of grid cells. Now both of these kinds of cells can make the place cells fire. And he can return to the location where he parked by moving so as to find where it is that best matches the firing pattern of the place cells in his brain currently with the stored pattern where he parked his car.

他可能憑藉與周邊建築以及四周邊界的相對距離和方向來回憶他的車停在哪兒。而那將由專門「檢測邊界」的神經元細胞發出的信號來執行。他可能也記得自己是怎麼從停車場走出來的，而這就有賴於網狀細胞發出信號了。這兩種類型的神經元細胞都可以激活「定位細胞」。因此荷馬成功折返的方法便是在走動中尋求與他之前停車時腦中所建立的信號集樣式最為匹配的一個腦中即時形成的信號集樣式。

And that guides him back to that location irrespective of visual cues like whether his car's actually there. Maybe it's been towed. But he knows where it was, so he knows to go and get it. So beyond spatial memory, if we look for this grid-like firing pattern throughout the whole brain, we see it in a whole series of locations which are always active when we do all kinds of autobiographical memory tasks, like remembering the last time you went to a wedding, for example.

而那就能將他領回「老地方」了，這個過程與最終的目標視物無關，不論他的車是否還在那兒他都能找到停車點。或許車已經被拖走了。但他仍然知道車原來停在哪，因此他會回到原位去取車。撇開「空間記憶力」而言，倘若我們單獨觀察這種網狀信號集在整個大腦中的活動情況，就會發現這種信號形式分布廣泛，每當我們需要回憶一些自己過去的經歷時這種網狀的信號形式就會活躍起來，譬如，當你試圖回憶上次參加婚禮的情況時。

So it may be that the neural mechanisms for representing the space around us are also used for generating visual imagery so that we can recreate the spatial scene, at least, of the events that have happened to us when we want to imagine them. So if this was happening, your memories could start by place cells activating each other via these dense interconnections and then reactivating boundary cells to create the spatial structure of the scene around your viewpoint. And grid cells could move this viewpoint through that space.

因此，表示我們周圍空間的神經機制也可能被用來產生視覺圖像，以便我們能夠重建空間場景，這樣當我們試圖回憶一個曾經置身其中的場面時，至少可以藉助想象而勾勒出整個場景。倘若事實果真如此，你的記憶可以從放置細胞開始，通過這些密集的相互連接相互激活，然後重新激活邊界細胞，以創建視點周圍場景的空間結構。網狀細胞可以使視點穿透那個空間。

Another kind of cell, head direction cells, which I didn't mention yet, they fire like a compass according to which way you're facing. They could define the viewing direction from which you want to generate an image for your visual imagery, so you can imagine what happened when you were at this wedding, for example. So this is just one example of a new era really in cognitive neuroscience where we're beginning to understand psychological processes like how you remember or imagine or even think in terms of the actions of the billions of individual neurons that make up our brains.

而另一種「方位細胞」，我之前沒有提到它，它們像指南針一樣，都是根據你的朝向來作出反應的。它們可以定義你想要為你的視覺圖像生成圖像的觀察方向，例如，你可以想象當你在這個婚禮上發生了什麼。這只是認知神經科學新時代的一個例子，在這個時代，我們開始了解心理過程，比如你如何記憶或想象，甚至是根據組成我們大腦的數十億個神經元的行動來思考。

Thank you very much.

非常感謝。